1. Field of the Invention
The present invention relates generally to viscometers and more particularly to a coupler for providing connection of an upper segment and a lower segment of a bob shaft of a co-axial viscometer.
2. Description of the Related Art
Rotating viscometers include, among other things, a bob suspended from a bob shaft, and a torque-measuring device. In operation the bob is positioned in a sample cup containing a sample fluid. The fluid sample is rotated in relation to the bob by rotation of the sample cup or a sleeve in order to determine properties of the sample fluid.
It is necessary from time to time to clean the bob, change the bob type, replace the bob, or repair the bob. The bob is commonly attached to the bob shaft through use of threading so that the bob is screwed on and off the bob shaft for cleaning, replacement, or repair. This prior art attachment method creates the possibility of human error including over and under tightening during replacement of a bob. Over tightening of a bob to a bob shaft can lead to seizure of the bob to the bob shaft as well as to the sensing parts of the equipment. Under tightening of a bob to a bob shaft can lead to release of the bob during operation. This prior art attachment can also lead to damage to the bob and/or bob shaft including damage to the threading itself.
Another prior art method of bob attachment is a taper bore fit of the bob shaft in a hollow bob. This attachment method creates the possibility of the bob falling off and even the potential of rupture or explosion if fluid gets trapped inside the hollow bob and is heated.
Exemplary rotating viscometers having bob shafts are described in U.S. Pat. No. 6,070,457 to Robinson, U.S. Pat. No. 6,571,610 to Raffer, U.S. Pat. No. 6,691,559 to Robinson, U.S. Pat. No. 6,951,127 to Hongfeng, U.S. Pat. No. 6,938,474 to Hongfeng and U.S. Pat. No. 7,287,416 to Hongfeng. The identified patents disclose various ways of attaching a bob to a bob shaft and/or a torsion wire, attaching a bob by use of threading of the bob and the bob shaft or by constructing the bob integral with the bob shaft.